Various systems are known in the art for detecting an object coordinates. Some of such systems are touch screens and blackboard inputting devices. These systems usually detect coordinates of a pointing instrument such as a pen, a fingertip or a special device designed for use with such system.
Among the methods of operation of such input devices are methods based on sensitivity to physic contact resistive layers, acoustical radiation, electromagnetic radiation, capacitive means and the like.
Among the non-touch system are optical systems that are able to detect two-coordinate position of an object. Some of these systems are based on one or two scanning devices attached to a blackboard or a computer display. Scanning systems are based on a rotating mirror or rotating light source emitting light beam that scans a thin space located in close proximity to the screen display or to the blackboard.
Some of these types of systems are comprised of a rotating half mirror emitting the scanning light beam and reflecting the returned light from an object placed in front of the device to a light sensitive device. Two such units may be used in order to be able to implement triangulation methods. Other methods use only one such unit with addition of mirrors surrounding part of the display frame, by analyzing the light reflections from these mirrors the coordinates of an object placed within the frame boundaries are found.
In U.S. Pat. No. 5,455,669 a similar scanner device is used operating on measuring the time of fight of a light beam transmitted to the object. One disadvantage of such scanning system is the need to have moving parts such as a mirror. These motor-based devices are suitable mostly for large blackboard inputting systems, and not so much for computer display monitor applications or virtual keyboard applications.
A device with stand-alone unit is described in U.S. Pat. No. 5,502,568. This device is based on a pen that is comprised of a special modulation circuit driving a light source embedded inside the pen. The usage of such system is limited because of the special pen circuit; it is not possible to use a simple object such as a regular pen or a human finger to operate the device.
Other types of such devices are based upon two light receiving units such as video cameras placed on various locations around the blackboard or the display unit. Such arrangement can be found in PCT International Publication No. WO 00/21023 or in U.S. Patent Application Publication No. 2001/0,030,642.
Similar types of devices are optical devices which are based on Charged Coupled Devices (CCD) or other photo sensitive sensors. These devices include a lens placed in front of the photo sensitive device inside each such unit. These units are placed on different locations on the blackboard or the display unit. The method of operation of such devices is based on triangulation analysis of the images that fall on the photo sensitive devices. Most of these systems usually contain an Infra Red (IR) light source and a matched spectral filter in order to filter ambient light noises.
U.S. Pat. No. 4,782,328 describes such two units which each are comprised of linear CCD and one wide viewing lens system in front of the CCDs. The wide-angle lens system enables viewing the plane above the display unit while each such unit is installed in close proximity to the display frame. Other two-unit systems are described in U.S. Pat. No. 6,421,042. This patent describes a two-unit system with one lens included in each such unit. In addition, a third coordinate measurement option is presented.
The main disadvantage of these two last patents is the fact that two units are needed in each system. Another disadvantage is the fact that in the first patent a wide-angle lens system is needed, and in the second patent only a limited viewing angle is possible thus, the units of such system need to be installed with some distance from a screen display frame.
As mentioned above additional usage of the embodiments is in implementation of a virtual keyboard.
Virtual keyboard applications are described in various patents. PCT International Publication No. WO 02/057714 A1 describes such system while using a method of measuring time of flight of a light that is projected on the user hands. By analyzing the three dimensional image received the system can determine the keystroke on the virtual keyboard.
Another virtual keyboard device is described in European Patent Application EP 1,248,227 A2 while using one viewing unit which comprises a complex optical device or two CCDs to project the same image from different viewing angles into the CCD/s.